1. Field of the Invention
The present invention relates to a molded package for a light emitting device, and a light emitting device using the same.
2. Description of the Related Art
Light emitting devices with alight emitting element, such as a LED, employs a ceramic package for effectively dissipating heat generated from the light emitting element. The ceramic package is a package including a ceramic substrate with a printed wiring on an upper surface thereof, and a circular resin wall rising from the upper surface of the ceramic substrate. The printed wiring includes a wiring for mounting the light emitting element, and a wiring for power feeding. The resin wall is disposed to enclose the wiring for mounting the light emitting element, and has a function of directing light from the light emitting element.
Ceramic has high heat conductivity as compared to general resin for packages, so that the ceramic package has excellent heat dissipation properties.
The ceramic used in the ceramic package has the excellent heat dissipation properties, but is expensive as compared to resin. Thus, a light emitting device using the ceramic package also becomes expensive. In order to reduce the amount of ceramic used, a package including a small-sized ceramic member embedded in a resin package is used to manufacture a light emitting device (Registered Utility Model No. 3109109 (Unity Opto Technology Co., Ltd.) and JP 2007-250979 A (Zeniya Industry Co., Ltd.)).
For example, Registered Utility Model No. 3109109 (Unity Opto Technology Co., Ltd.) discloses a solid semiconductor light emitting element (light emitting device) includes a ceramic heatsink block having a protruding mount cup with a light emitting element (chip) mounted thereon, and a coupling base formed by insert-molding a lead frame with resin. The lead frame includes a first sub-lead, a second sub-lead having the same shape as that of the first sub-lead, and a third sub-lead having a through hole and coupled to the first sub-lead. The coupling base has another through hole in a position corresponding to the third sub-lead. The mount cup of the heatsink block is fitted into the through hole of the coupling base, which integrates the heatsink block and the coupling base together.
The resin material (hereinafter referred to as a “resin protrusion”) is protruded around the through hole of the coupling base so as to cover the third sub-lead to be abutted against the side surface of the mount cup of the heatsink block.
JP 2007-250979 A (Zeniya Industry Co., Ltd.) discloses a light emitting diode package with a reflection cup formed of a white resin around a lead frame integrated with the surface of a heat dissipation ceramic by brazing. The light emitting element (LED) is mounted on the lead frame, or on the heat dissipation ceramic exposed from the lead frame.
In the light emitting device disclosed in Registered Utility Model No. 3109109 (Unity Opto Technology Co., Ltd.) and JP 2007-250979 A (Zeniya Industry Co., Ltd.), the light emitting element is mounted on the ceramic member, which can effectively dissipate the heat generated from the light emitting element via the ceramic member. Upon mounting the light emitting device on a mounting board, a lead of a resin package can be used to mount the light emitting device by reflow soldering.
In the technique disclosed in Registered Utility Model No. 3109109 (Unity Opto Technology Co., Ltd.), the first sub-lead and the second sub-lead are exposed to the outside (at a ring-like recess) with respect to the resin protrusion provided around the through hole of the coupling base. The third sub-lead is covered with the resin protrusion. Thus, in order to perform wire-bonding on a chip to the sub-lead, a long wire leading from the protruded mount cup to the ring-like recess is necessary. However, the long wire is likely to be broken in sealing with a seal resin or the like, or increases the amount of wire used, which is not preferable.
In the technique disclosed in JP 2007-250979 A (Zeniya Industry Co., Ltd.), the ceramic and lead frame are heated at high temperature (for example, 760° C.) when fixing the heat dissipation ceramic to the lead frame by brazing. Thereafter, during cooling, the lead frame contracts more than the ceramic due to a difference in thermal expansion coefficient. The lead frame largely contracts to pull the ceramic from both side surfaces, which might cause cracks. In order to prevent the cracks, a relatively soft lead frame having hardness Hv of 40 to 80 is preferably used. The soft lead, however, warps largely in heating, and might be peeled out of a molding resin, which makes it to industrially use the soft lead.